Optical Demultiplexer by Using In-Line Fiber Filter

Abstract

The signal pulses will be broadened through the fiber and so we need a very sharp cutoff filters with demultiplexers. The in-line fiber filter becomes the appropriate filters. Most of these demultiplexers used after erbium-doped fiber amplifier (EDFA) which need a sharp wavelength bandpass filter (BPF) to filter out wavelengths other than the signal wavelength Exact analysis of in-line fiber filter is occurred by derive a polynomial expression for the dopant ratios of GeO2 and P2O5. The refractive index of silica doped either GeO2 or P2O5 is defined as a function of both the wavelength and the dopant ratio. The calculations of the dopant ratios of the pair materials (GeO2 and P2O5) are done at a specific filter cutoff wavelength (λc) for both high pass filter (HPF) and low pass filter (LPF). Two in-line fiber filters (HPF and LPF) are cascaded to make a sharp bandpass filter (BPF). The length of in-line fiber filter must be very short to overcome the weak of the propagation constsnt throuh it. The normalized frequency is discused. A theoritical 8-channels demultiplexer is done. The design of demultiplexer becomes very easy.